1. Field of the Invention
This present invention is related to an insulated gate bipolar transistor (IGBT) with a fast reverse recovery time rectifier having and a manufacturing method thereof, and more particularly, to an IGBT with a rectifier having fast reverse recovery time for speeding up the reverse recovery of the rectifier and a manufacturing method thereof.
2. Description of the Prior Art
An IGBT is regarded as a composite structure combining a metal-oxide-semiconductor field effect transistor (MOSFET) and a bipolar junction transistor (BJT). By combining the MOSFET's characteristic of easy control with a gate electrode and the BJT's characteristic of low turn-on voltage drop, the IGBT is widely applied in high voltage and high power applications.
Please refer to FIG. 1. FIG. 1 is a cross-sectional diagram illustrating a conventional IGBT. As shown in FIG. 1, the conventional IGBT 10 is described as follows. First, an N-type buffer layer 14 is formed on a P-type semiconductor substrate 12, and an N-type epitaxial layer 16 is formed on the N-type buffer layer 14 to serve as a drain electrode of a parasitic MOSFET in the IGBT 10. Then, two gate structures 18 are formed in the N-type epitaxial layer 16. Each gate structure 18 includes a gate electrode 20 and a gate insulating layer 22 for electrically isolating the gate electrode 20 and the N-type epitaxial layer 16. Subsequently, a P-type doped base region 24 is formed in the N-type epitaxial layer 16 between two gate structures 18, and two N-type doped source regions 26 are formed in the P-type base region 24 to separately contact with each gate insulating layer 22 and to serve as source electrodes of the parasitic MOSFET in the IGBT 10. Following that, a dielectric layer 28 is formed on the N-type epitaxial layer 16, the P-type base region 24 between two N-type doped source regions 26 is uncovered, and a P-type doped contact region 30 is formed in the uncovered P-type base region 24. Then, an emitter metal layer 32 is formed to cover the dielectric layer 28, the P-type doped contact region 30, and the N-type doped source region 26. Finally, a collector metal layer 34 is formed below the P-type semiconductor substrate 12.
Conventionally, the IGBT is formed on a substrate by the aforementioned semiconductor manufacturing technology. Then, the IGBT is electrically connected to an external diode for providing a rectifier function, so that the circuit component of IGBT and the diode component can be packaged in the same package structure. However, the structure, which includes IGBT connected to an external diode, has higher production cost, more complicated packaging, and is large in size, so it does not conform to a trend of high degree of precision for electronic components.
Therefore, in order to improve the degree of precision for electronic components, a method is presently utilized in the industry and is described as follows. An N-type doped cathode region is formed in the P-type semiconductor substrate of the IGBT, and the N-type doped cathode region is electrically connected to the N-type epitaxial layer and the collector metal layer, wherein the N-type epitaxial layer serves as a cathode of the diode and the P-type base region serves as an anode of the diode. Thus, the diode component can be integrated in the same integrated circuit structure by parasitizing the diode component in the IGBT. A PN junction is formed between the P-type base region and the N-type epitaxial layer, the electron carriers in the N-type epitaxial layer near the P-type base region may be injected into the P-type base region, and the hole carriers in the P-type base region near the N-type epitaxial layer may be injected into the N-type epitaxial layer, so that a depletion region is formed between the P-type base region and the N-type epitaxial layer. However, when the bias of the diode switches from the forward bias to the reverse bias, i.e. the IGBT is under the voltage-sustaining state, the depletion region of the PN junction may enlarge, i.e. to drive out the hole carriers which are injected in the N-type epitaxial layer or to exclude the excess minority carriers in the depletion region. Accordingly, reverse recovery time is required, so that the switching speed of the integrated structure of the IGBT and the diode is limited. Because the IGBT is a high voltage component which is above 600 Volts, a very thick N-type epitaxial layer is required to serve as a voltage-sustaining layer. As a result, how to decrease the injection of the excess minority carriers and improve the switching speed of an integrated structure of an IGBT and a rectifier by new structure design is an important issue in the industry.